There are additional categories of evidence that fall under the purview of evidence law pertaining to how evidence is obtained and what impact it has on the lawsuit in which it is introduced. These other sorts of proof will be examined briefly in this article

How Did You Get That?

On occasion, there is evidence that can greatly assist or seriously harm a given side in legal proceedings--evidence that is quite relevant to the matter at hand. However, this evidence, no matter how relevant, is sometimes deemed inadmissible. The reason for this type of ruling hinges on this fact: the manner in which evidence is obtained is every bit as important as the content and relevance of that evidence. This section addresses the topic of evidence that is illegally obtained (and therefore inadmissible in court).

Illegally obtained evidence applies to criminal cases only and is typically "evidence acquired by violating a person's constitutional protection against illegal searches and seizures; evidence obtained without a warrant or probable cause" (Blackwell, 2004). This ties in with the legal principle known as the exclusionary rule, which states "evidence collected or analyzed in violation of the U.S. Constitution is inadmissible for a criminal prosecution in a court of law (that is, it cannot be used in a criminal trial)". This provision was developed to provide maximum protection of an individual's rights and civil liberties and to ensure that law enforcement procedures are conducted properly.

The exclusionary rule was established at the federal level in 1914 by the United States Supreme Court in the case Weeks v. United States, 232 U.S. 383. Until that time, the common law provided that any relevant evidence, no matter how it was obtained, could be entered into criminal proceedings as proof. Simply put, this rule disallowed the use of any evidence that was obtained by illegal means. A further case, Mapp v. Ohio 367 U. S. 643, in 1961, made the rule applicable and binding to the states. Other cases pertaining to this rule include Wolf v. Colorado (1949), United States v. Leon (1984), and Pennsylvania Board of Probation and Parole v. Scott (1998). It currently applies to all citizens and resident aliens within the United States.

The primary function of the exclusionary rule is to deter law enforcement officials and others from gaining evidence in an unlawful manner (i.e., as prohibited in the Fourth and Fifth Amendments to the United States Bill of Rights). These amendments protect citizens from unreasonable searches and seizures and compelled self-incrimination, respectively. This rule does not apply, though, to civil cases, nor to cases involving aliens that reside outside the United States (see United States v. Alvarez).

Exceptions to the Exclusionary Rule

As with all rules, there are exceptions, and the exclusionary rule is no different. Several notable caveats and provisos apply. First, even when the rule applies, it only excludes illegally obtained evidence for the purpose of proving the defendant's guilt forthe particular crime.Such proof can still be used to impeach the credibility of the defendant's trial testimony. However, if the defendant doesn't testify, this loophole cannot be used.

Another exception is the inevitable discovery doctrine, established in the Nix v. Williams case of 1984, which "holds that evidence obtained through an unlawful search or seizure is admissible in court if it can be established, to a very high degree of probability, that normal police investigation would have inevitably led to the discovery of the evidence". In the case People v. Stith, the court ruled that such evidence could be admitted under this doctrine, but only as secondary evidence. Primary evidence, or "the best and most important evidence in a case" (Blackwell, 2004), was still bound by the conditions of the exclusionary rule.

Third, the attenuation exception is that "evidence may be suppressed only if there is a clear causal connection between the illegal police action and the evidence". In other words, unless it can be proven that the evidence resulted directly from some illegal action taken by law enforcement officials, it can be admitted. In People v. Martinez, a three-part test was established for this exception: "(1) the time period between the illegal arrest and the ensuing confession or consensual search; (2) the presence of intervening factors or event; and (3) the purpose and flagrancy of the official misconduct".

A fourth is the independent source exception, which allows evidence into proceedings if it came from a knowledgeable and independent source. In this sense, an independent source must be someone utterly unconnected to the illegality of the arrest, search, and/or seizure (People v. Arnau).

Finally, there is good faith exception, which permits the admission of some illegally obtained evidence if it is the result of a minor or technical error. For example, if "a magistrate is erroneous in granting a police officer a warrant, and the officer acts on the warrant in good faith, then the evidence resulting in the execution of the warrant is not suppressible". The good faith exception does not apply in all such situations, however. Specifically, "(1) no reasonable officer would have relied on the affidavit underlying the warrant. (2) the warrant is defective on its face for failing to state the place to be searched or things to be seized. (3) the warrant was obtained by fraud on the part of a government official. (4) The magistrate has "wholly abandoned his judicial role'".

Courts located outside the United States have, on the whole, not subscribed to or have abandoned the exclusionary rule and the conceptual framework behind it. This may be, in part, due to the fact that the United States' Bill of Rights has explicit provisions protecting the privacy and integrity of individuals and other countries do not have an analogue in their founding documents. Whatever the case, the exclusionary rule is something that is unique to the American justice system in trying criminal cases.